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High performance RF MEMS metal-contact switches and switching networks

  • Author(s): Patel, Chirag D.
  • Patel, Chirag D.
  • et al.
Abstract

This dissertation presents the design and measurement of high performance RF MEMS metal contact switches capable of achieving mN-level contact and release forces. The switches are designed and demonstrated to be tolerant to a wide range stress effect and temperature. Chapter 2 presents an electrostatic RF MEMS metal contact switch based on a tethered cantilever topology. The use of tethers results in a design that has low sensitivity to stress gradients, biaxial stresses, and temperature. A switch with a footprint of 160x190 [mu]m² and based on a surface-micromachined 8-[mu]m thick gold cantilever with a Au/Ru contact is implemented on a high-resistivity silicon substrate and results in a total contact force of 0.8-1.2 mN at 80-90 V, a restoring force of 0.5 mN, a pull-in voltage of 61 V, an up-state capacitance of 24 fF, and an actuation time of 6.4 [mu]s. The device achieves a switch resistance of 2.4±1.4 Ohms to 1.8±0.6 Ohms at 90-100 V in open laboratory environments (unpackaged). Chapter 3 presents a temperature stable metal-contact RF MEMS switch capable of handling >5W of RF power (a second generation of the tethered cantilever topology). The device achieves 0.7 - 1.5 mN of contact force for actuation voltages of 80 - 90 V, with a restoring force of 0.63 mN. Furthermore, the device is insensitive to stress effects and temperature. Temperature measurements showed excellent thermal stability - no deflection in the beam, and a change in pull-in voltage of only 4 V from 25-125°C. The switch was tested under prolonged (>24 hrs) high-power RF conditions with excellent reliability. Chapter 4 presents a compact RF MEMS metal-contact switch based on a tethered cantilever topology and orthogonal anchors. The switch is a "medium-force" design capable of achieving 0.38-0.72 mN of contact force for actuation voltages of 90-100 V and a restoring force of 0.46 mN (simulated) in a 120160 um^2 area. The pull-in and release voltages are 75 V and 70 V, respectively. In the down-state, the switch resistance is 1-2 with a Au/Ru hybrid contact. In the up-state, the capacitance is 16 fF, resulting in an isolation of 20 dB at 10 GHz and 9 dB at 40 GHz for an SPST configuration. Furthermore, the switch demonstrated a reliability of >10 million cycles (1 W, cold switching) and a power handling of >5 W. For a series/shunt configuration, the switch achieves an isolation of 55 dB at 10 GHz and 35 dB at 40 GHz. Compact SP4T and SP6T switching networks are also implemented. The SP4T is 850x530 [mu]m² (850x650 [mu]m² with bias pads); the SP6T is 850x730 [mu]m² (850x855 [mu]m² with bias pads). Both designs achieve an isolation ~36 dB and insertion loss < 0.3 dB at 3 GHz. Chapter 5 presents a mN-level contact and restoring force RF MEMS metal-contact switch exhibiting high reliability, high linearity, and high power handing for DC-40 GHz applications. The device, which is insensitive to stress and temperature effects, achieves 1.2-1.5 mN of contact force (per contact) from 80-90 V and 1.0 mN of restoring force (per contact). The up-state capacitance is 8 fF, resulting in an isolation of -46, -31, and -14 dB at 1, 6, and 40 GHz, respectively. Measured results show switch resistances of 1-2 Ohms and a reliability of >100 million cycles at 2-5Wunder cold-switching at 100 mW under hot- switching conditions, in an unpackaged and standard laboratory environment. Furthermore, the device was tested under prolonged hold-down conditions and demonstrated excellent RF power handling (>10 W) and DC current handling (>1 A) capability. Finally, SP4T and SP6T switching networks implemented with the metal-contact switch are demonstrated

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